Expressing apparatus



Dec. 24, 1957 T. ONARHEIM ETAL 2,817,287

EXPRESSING APPARATUS Filed Nov. .4, 1953 BEA EXPRESSED? G APPARATUS Thor Onarheini and Peder Solheim, Kaarevik, Norway, assignors to A/ S Stord, Stord, Norway Application November 4, 1053, Serial No. 390,142 6 Claims. (Cl. 100-50) This invention relates generally to apparatus of the type used to express liquor-containing materials, and is particularly directed to screw presses of the kind wherein the pressure exerted upon the materials within the press is obtained, at least in part, by arranging the screw within the press in such a way that the thread volume, that is, the volume of the space contained between the threads, from the inlet towards the outlet of the press, is gradually reduced, so that the materials are subjected to a continuously increased pressure while being conveyed along the press by the action of the rotating screw.

Usually, such reduction in thread volume is obtained either by tapering the shaft of the screw gradually outwardly from the inlet end toward the outlet end, or by arranging the tlneads with gradually reduced pitch from the inlet end toward the outlet end. In either case the screw is enclosed within a cylindrical, perforated casing.

An object of the invention is to provide an improved type of continuous screw press, wherein the screw is axially displaceable or reciprocable within the press casing by means of a hydraulic system.

Another object is to provide means for regulating the volume reduction of the materials within the press in accordance with the torque transmitted to the screw, so that the torque does not become excessive when operating on materials which are not easily pressable.

A further object of the invention is to counterbalance the axial thrust of the screw by means of hydraulic fluid, so that the thrust will not exceed a predetermined value.

The above, and other objects, features and advantages of the invention will be apparent in the following detailed description of illustrative embodiments thereof, presented merely by way of example, and which are shown in the accompanying drawings forming a part hereof and wherein:

Fig. 1 is an axial sectional view of an paratus embodying the present invention, trol or regulating system thereof being ly; and

Fig. 2 is a schematic View of another control or regulating system embodying the present invention and which may be used as an alternative to the system of Fig. 1.

Referring to the drawing in detail, and initially to Fig. 1 thereof, it will be seen that an expressing apparatus embodying the present invention includes an outer casing 1 enclosing a perforated, cylindrical press casing 2 which is supported within the outer casing by supporting rings 3. The press casing 2 encloses or defines an interior pressing space 4, within which a pressing screw is rotatably and slidably mounted. The outer casing 1 is provided with an inlet hopper 7 opening into an inlet portion 6 of the space 4 and into which the material to be expressed is fed. Such material is then carried forward by the screw 5 through the pressing space 4. In the inlet portion 6 a preliminary pressing takes place during which a substantial portion of the liquid content of the material is liberated, such liquid being collected in the bottom of an annular space 8 between the outer casing expressing apwith the conshown schematical- 2,817,287 Patented Dec. 24, 1957 1 and press casing 2 and drained therefrom through a liquid outlet 9.

The screw 5 includes a hollow shaft 10, which gradually tapers outwardly or increases in diameter from the inlet end to the outlet end of the press, said shaft having a helical thread 11 thereon to convey the materials along the length of the pressing space 4 from the inlet portion 6 to an outlet opening 12 at the end thereof remote from the hopper 7. The outlet opening 12 is covered by a plate 13, which is urged axially against the opening 12 by a compression spring 14. At the outlet end of the press, the screw 5 is mounted slidably on a hollow stub shaft 15 which accommodates a condensate pipe 16 extending throughout the length of shaft 15 and having its inner end bent into a gooseneck 17 to the bottom of the hollow interior 18 of the screw 5. In order to heat the material being expressed, steam may be supplied from a suitable source (not shown) through the hollow stub shaft 15 to the interior 18 of the hollow shaft 10 of the screw 5, while condensate may be removed from the interior 18 through the pipe 16.

The shaft 10 of expressing screw 5 is keyed, or otherwise secured, as at 15a, to stub shaft 15 for rotation with the latter while being free to move axially relative to the perforated casing 2. The stub shaft 15 is mounted in suitable bearings 19 and has a spur gear 20 fixedly mounted thereon and meshing with another spur gear 21 which has a greater axial length so that the gear 20 can move axially with the stub shaft 15 while maintaining meshing engagement with the gear 21. The gear 21 is driven, through a belt and pulley transmission 22, by a suitable electric motor 23.

After liquid has been expressed from the material to a certain degree in the inlet portion 6, the materialris further conveyed through the pressing space 4 and expressed by the decreasing thread volumes along the length of the screw towards the outlet opening 12 where the press cake bears against the cover 13 and raises the latter from its seat against the action of the spring 14. Thus, the press cake automatically unseats the cover 13 to permit removal of the press cake through the outlet opening 12.

The thread volumes at different points along the screw 5 are given a certain ratio of taper, known as the press characteristic of the screw in question. The most desirable ratio of taper of the screw differs substantially for diiferent materials to be pressed, so that for different materials, different thread volumes should be used in the press, to obtain proper pressing.

Usually, when pressing different materials, it has been necessary to employ different presses, or interchangeable screws in one press, having different pressing characteristics. Presses exist wherein only a part of the screw may be exchangeable, the intention thereof being that the pressing characteristics of such screw may be changed without exchanging the entire screw. Further, it has previously been proposed to provide a press screw which is adjustable in the longitudinal direction in relation to its surrounding casing, whereby the material may be introduced into the press at a part of the screw having a thread volume which may be either increased or reduced, whereby the pressing characteristics of the press are changed correspondingly.

However, the heavy shaft thrust, which arises during the pressing operation, has limited the practical use of the last mentioned proposal, as such axial thrust in large presses may reach considerable heights. Thus, the axial adjustment of the press screw by manually operated mechanical means, as heretofore suggested in the art, is only possible in small presses with small pressing capacities.

As distinguished from the above, the press according to the present invention is arranged with an axially adjustable screw, wherein the axial adjustment of the screw is effected by hydraulic means, as shall be hereinafter described in detail.

According to the present invention, the screw 5 carries a piston 24 at one end reciprocable in a cylinder 25 which is arranged coaxially to the screw 5 and its pressing space 4 at the inlet portion 6 thereof. The piston 24 is, in the illustrated embodiment of the invention secured to the entrance end of the press screw 5 by bolts 26 and rotates in unison therewith.

Pressure fluid is supplied to the end of the cylinder 25 through an inlet pipe 27 and discharged from the cylinder through an outlet pipe 28, so that a positive pressure may be applied axially to the screw 5 by means of pressure fluid acting against the piston 24 and supplied from a pump 29 which is driven by a motor and interposed in the inlet pipe 27. A reservoir for the hydraulic or pressure fluid is indicated at 31, and a choke valve 32 is interposed in the return or outlet pipe 23 and adapted to control the pressure within the cylinder 25 by metering the return flow from the cylinder to the reservoir.

Further, by-pass valves 37a and 37b are interposed in the inlet and discharge pipes 27 and 28 between the cylinder and the pump 29 and metering or choke valve 32, respectively. The by-pass valves 37a and 37!) are arranged to permit flow of the pressure fluid to and from the cylinder 25 through the related pipes 27 and 28, when the valves are positioned as shown in the drawing, and to cut-off the cylinder 25 from the pump 29 and the return to reservoir 31, when the valves 37a and 3712 are rotated 90 from their illustrated positions, with the valves in their above mentioned rotated positions being effective to return the pumped fluid to the reservoir through a by pass pipe 370. Thus, when the valves 37a and 371; are rotated to by-pass the pressure fluid through the pipe 37c, the pressure fluid within the cylinder 25 is trapped in the latter and being substantially inelastic maintains the screw 5 in a fixed axial position even though the axial thrust reaction of the screw 5 may vary when pressing different materials.

However, when the valves 37a and 37b are in the positions illustrated in the drawing, adjustment of the choke valve 32 to vary the resistance to return flow of pressure fluid through discharge pipe 28 will effect adjustment of the pressure in the cylinder 25 for moving the screw 5 axially, either to the left or to the right, as viewed in the drawing, depending upon whether the force exerted against piston 24 by the pressure in cylinder 25 is greater than or less than the axial thrust reaction of the screw 5. Thus, the axial position of the screw 5 will be determined by a balance of the axial thrust reaction and the force exerted against the piston 24. If during operation of the apparatus the axial thrust reaction on the screw 5 varies from its normal value, as, for example, when the material being expressed is not homogeneous, the screw 5 is automatically displaced axially to compensate for the momentary or permanent change in the character of the material being expressed. Thus, if the material fed to the hopper 7 becomes more fluid or more easily compressed, the resistance of the material to compression during movement along the screw 5 is correspondingly reduced and the axial thrust reaction on the screw is lowered so that the pressure in cylinder 25 causes movement of the screw 5 towards the left, as viewed in the drawing. Such movement of the screw 5 places a smaller diameter portion of the screw shaft 10 opposite the hopper 7 and increases the difference between the thread volumes at the inlet and outlet ends to cause a corresponding increase in the amount of liquid expressed from the material until the force exerted against piston 24 by the pressure fluid is again balanced by the axial thrust reaction on the screw 5. On the other hand, if the resistance to compression of the material fed into hopper 7 is increased, the axial thrust reaction on screw 5 is increased and overpowers the tit force exerted by the pressure fluid against piston 24 thereby causing axial displacement of the screw 5 toward the right, as viewed in the drawing. Such axial movement of the screw 5 increases the diameter of the screw shaft 10 opposite the hopper 7 and thereby decreases the difference between the thread volumes at the inlet and outlet ends to cause a corresponding decrease in the axial thrust reaction until that reaction is balanced by the force of the pressure fluid in cylinder 25.

Thus, with the valves 37a and 37b disposed as in the drawing, the described apparatus automatically subjects the material fed to the hopper 7 to a constant pressure force determined by the pressure in cylinder 25, which is preferably as high as possible to obtain the maximum removal of liquid from the material.

Further, by setting the choke valve 32 in a position giving a pressure in cylinder 25 great enough to overcome any axial thrust reaction on the screw 5 which might be realized under normal operating conditions, the screw 5 will be moved to its extreme position to the left and it will be displaced from that extreme position only by exceptional axial loads to prevent damage to the apparatus thereby acting as a safety device.

On the other hand, when the valves 37a and 37b are rotated to trap the pressure or hydraulic fluid in cylinder 25 and thereby to fix the axial postion of the screw 5, the material will be subjected to a constant volume reduction which may be adjusted by varying the axial position of the screw 5 prior to trapping of the pressure fluid in cylinder 25.

When processing oil-containing materials, the oil extracted therefrom may be employed as the hydraulic fluid fed to the cylinder 25 and then leakage of oil past piston 24 will not be objectionable unless such leakage is great enough to prevent the maintenance of the necessary pressure within cylinder 25.

In the apparatus illustrated in the drawing and embodying the present invention, the motor 23 is energized from a main current supply 33 through suitable conductors 34 having a wattmeter 315 interposed therein to measure the power absorbed by the motor. It is apparent that the power absorbed by the motor 23 will vary with the resistance to rotation of the screw 5, and hence will be a function of the compressibility of the material fed into the hopper 7.

In accordance with the present invention means actuated by the wattmeter 35 are provided for controlling the position of the choke or metering valve 32 so that, when the resistance to turning of the screw 5 and the power absorbed by the motor 23 are increased, the valve 32 is rotated in the direction relieving the obstruction to fluid flow through return or discharge line 28 thereby to reduce the pressure in cylinder 25 and to effect movement of screw 5 toward the right, as viewed in the drawing, and to decrease the difference in the thread volumes at the inlet and outlet which tends to reduce the resistance to rotation of the screw 5. Conversely, a decrease in the resistance to the rotation of screw 5 and in the power absorbed by motor 23 would be translated into an increase in the pressure in cylinder 25 for effecting movement of screw 5 to the left and a corresponding increase in the difference between the thread volumes at the inlet and outlet ends.

In the illustrated embodiment, such means for controlling the valve 32 includes an electric servo-system or mechanism, generally identified by the reference numeral 36, and including the usual synchro-gencrator 36a, having its rotor coupled to the wattmeter 35 to be rotationally positioned by the latter, and a synchro-motor 36b electrically connected in the usual manner to the rotor R and stator S of the synchro-generator 35a with its rotor R being operatively coupled to the valve 32, as by the gearing 32a, to rotate the valve member in response to displacement of the wattmeter by changes in the power absorbed by motor 23. If desired, a hand-wheel 32b may be provided for manual actuation of valve 32' either to over-ride the automatic control described above or for use when such automatic control is inoperative.

While the piston 24 is shown fixedly secured to the screw 5 and moves with the latter both rotationally and axially, it is to be understood that such an arrangement is not necessary in an embodiment of the present invention and that the piston 24 can be merely axially coupled to the screw 5 with the latter being free to rotate relative to the piston which can be restrained against rotation within the cylinder 25. Further, while the difference between the thread volumes at the inlet and outlet ends of the screw 5 is obtained in the illustrated embodiment by providing a tapered screw shaft it is apparent that the same results can be obtained with a cylindrical shaft having a helical worm, corresponding to the worm 11, in which the pitch between successive turns decreases from the inlet to the outlet end of the screw or conveyor.

Referring now to Fig. 2 of the drawings, another control or regulating system is there illustrated and serves to adjust or vary the hydraulic pressure supplied to the cylinder 25 so that an increase in the axial thrust reaction on the screw 5 will produce a corresponding increase in the hydraulic pressure for maintaining the screw member in a fixed axial position. In Fig. 2, only the control or regulating system has been illustrated, and it is to be understood that an expressing apparatus, of the kind described in connection with Fig. l, is to be employed therewith. The control or regulating system of Fig. 2 includes a supply pipe 27, a discharge pipe 28, a pump 29 driven by a motor 30, a reservoir 31 and a choke or metering valve 32, all functioning in the same manner as the elements bearing corresponding reference numerals on Fig. 1. The valve 32 is actuated through gearing 320 by the synchro-motor 36b of an electric servo-mechanism 36, while the synchro-generator 36a of that mechanism has its rotor driven by a lever arm 38 which is connected by a link 39 to one end of a lever 40', pivoted intermediate its ends, as at 41, and having its other end constrained between collars 42 and 43 on the shaft of the expressing apparatus for axial movement with the expressing screw (not shown).

The elements of Fig. 2 are arranged so that, when shaft 15 moves to the right as a result of an increase in the axial thrust reaction, the lever 40 is rocked in the direction causing closing of the valve 32 to increase the pressure supplied to the hydraulic cylinder (not shown) through the pipes 27 and 28, and conversely, to effect opening of the valve 32 in response to the movement of shaft 15 to the left, so that the shaft 15, and the expressing screw (not shown), will tend to remain in a fixed axial position.

While particular embodiments of the present invention have been described in detail herein and shown in the drawings, it is to be understood that the invention is not limited to those particular embodiments, and that various changes and modifications may be effected therein without departing from the scope and spirit of the invention as defined in the appended claims.

What is claimed is:

1. In an expressing apparatus for processing liquid containing materials; the combination of a perforated cylindrical casing having a radially extending inlet opening adjacent one end thereof through which the material to be expressed may be introduced and an outlet opening at the other end for discharge of a solid cake after removal of the liquid from the material, a screw member rotatably and axially slidably mounted within said perforated casing and having a decreasing thread volume in the direction towards said outlet opening so that axial displacement of said screw member relative to said casing serves to vary the amount of thread between said inlet and said outlet openings, a housing around said perforated casing to receive and collect liquid expressed from the compressed material, means for rotating said screw member in such a direction as to cause movement of material fed into said inlet towards said outlet opening, a cylindrical portion forming a continuation of said inlet end of the casing to receive the end of the screw member when moved in a direction away from said outlet opening, a piston arranged at the inlet end of said screw member and having a diameter substantially equal to the diameter of said perforated casing and said continuation, said piston being received within said continuation so as to define a space for receiving hydraulic fluid, and means for supplying pressure fiuid to said space so as to provide a force acting towards the outlet end of said casing on said screw member through said piston.

2. In an expressing apparatus, the combination according to claim 1, wherein said means for supplying hydraulic fluid to said space comprises a hydraulic system comprising a pump, a reservoir for hydraulic fiuid coupled to said pump, a supply line extending from said pump to said space, a return line from said space to said reservoir, and an adjustable choke valve interposed in said return line for determining the maximum pressure in said space.

3. In an expressing apparatus, the combination according to claim 2, wherein said system further includes means operative to control said adjustable choke valve so that the pressure in said space is maintained at a constant value.

4. In an expressing apparatus, the combination according to claim 2, wherein said means for rotating the screw member includes an electric motor, means for supplying electric power to said motor, and means rotationally coupling said motor to said screw member, means connected to said power supply means and arranged to sense the power consumed by said motor in rotating said screw member, and an electric servo-mechanism being connected between said sensing means and said choke valve to adjust the latter in response to changes in the power consumed by said motor.

5. In an expressing apparatus, the combination according to claim 2, wherein said system further includes means operative to control said adjustable choke valve so that said screw member is maintained at a predetermined axial position.

6. In an expressing apparatus, the combination according to claim 1, wherein the material fed to said inlet opening contains a substantially incompressible liquid to be expressed therefrom, and wherein the medium of the hydraulic pressure used in the hydraulic system is the same liquid as that contained in the material to be expressed whereby leakage of the liquid from said cylinder past said piston can occur without contaminating the material to be expressed.

References Cited in the file of this patent UNITED STATES PATENTS 1,421,282 Meakin June 27, 1922 2,044,564 Carter June 16, 1936 2,109,398 McNitt Feb. 22, 1938 FOREIGN PATENTS 42,830 Norway May 10, 1926 102,603 Switzerland Dec. 17, 1923 266,966 Switzerland Feb. 28, 1950 560,184 Germany Sept. 29, 1932 

